The invention relates to a liquid crystal display comprising one LCD module, polarizers on both surfaces of the LCD module, reflector surfaces and a display control unit.
Liquid crystal displays, or LCDs, are used in a plurality of different devices such as watches, radios, calculators, portable computers and mobile phones, to list a few. FIG. 1 illustrates as an example the structural and operating principles of a conventional LCD. At the core of the LCD there is a liquid crystal layer between two layers of glass, where the orientation of the crystals is affected by transparent electrodes on the inner surfaces of the glass layers. These layers constitute the LCD module 10 of this presentation. On both surfaces of the LCD module there are polarizers 12 to polarize the light hitting the surface of the module. Placed against the outer surface of one of the polarizers is a reflector surface 14, reflecting back the rays of light arriving through the polarizers and LCD module. By conducting an electric current to the electrodes in the LCD module it is possible to orientate the liquid crystals in such manner that part of the polarized rays of light will not pass through the LCD module, whereby a pattern will become visible on the display. To improve the visibility of the pattern on the liquid crystal display there may additionally be a light guide 16 between the reflector surface and polarizer to provide a backlight which improves the visibility of the picture displayed, if necessary. The various component parts of LCDs, such as LCD modules, polarizers, reflector surface, and light guides, are commercially available parts and components known from the prior art, so they will not be described in more detail in this presentation.
As mobile phones in particular have become functionally more complex, it has become necessary to have telephone displays that can be viewed from different directions. Thus phones need to be equipped with several discrete liquid crystal displays, which naturally increases the manufacturing costs of the phone and adds to its weight and size. Publication GB 2343324 discloses a mobile phone in which there are LCDs on both sides of a hinged lid. In this solution the LCDs are placed on exactly the same location on the opposing sides of the lid so that the LCDs can share a xe2x80x9ccommonxe2x80x9d reflector surface. In this solution, too, there are two distinctly separate LCDs, installed against each other so that their viewing directions are on different sides of the lid. Use of a shared reflector surface cannot considerably reduce the manufacturing costs of a phone.
An object of the invention is to provide a liquid crystal display with a novel structure, viewable from two opposing directions, thus reducing the need for a plurality of separate liquid crystal displays.
A liquid crystal display according to the invention is characterized in that which is specified in the independent claim. Advantageous embodiments of the invention are presented in the dependent claims.
A liquid crystal display according to the invention has one LCD module with polarizers on both sides thereof. To generate the picture for the LCD module the display includes a control unit to control the electric current to the electrodes of the module. In this presentation, a xe2x80x9cpicturexe2x80x9d refers to all visual material to be shown on the display: graphic images, moving images, text or animation, for example. The display additionally includes, in a known manner, reflector surfaces to reflect rays of light into the viewing direction through the polarizers and LCD module. The display may further include light guides placed between the polarizers and reflector surface to provide a backlight for the display. A backlight is important especially in LCDs which are used in poor lighting conditions. A basic idea of the invention is that reflector surfaces are provided on opposing sides of the LCD module. Thus there are provided in the same LCD module sub-displays viewed from opposing directions on the different sides of the LCD module.
In an advantageous embodiment of the invention the reflector surfaces are placed on different sides of the LCD module in a fixed manner. In that case their sizes are such that they only cover part of the total area of the LCD module.
In a second advantageous embodiment of the invention a reflector surface and light guide constitute a movable unitary lid covering the surface of the LCD module in whole or in part. A sub-display is then formed on that side of the LCD module where the lid is opened.
In a third advantageous embodiment of the invention the control unit is programmed so as to generate the picture on a sub-display in such a manner that the picture is always the right side up when viewed from the direction of viewing. In practice this means that a picture generated for the viewing direction of a first sub-display is converted, by a program, into a mirror image when viewed from the viewing direction of a second sub-display.
An advantage of the invention is that it reduces the number of materials and components needed to build displays and therefore reduces material costs compared to building two separate displays.
Another advantage of the invention is that the time needed to manufacture and install displays becomes shorter as only one display is needed instead of two separate displays.
A further advantage of the invention is that the total space requirement and weight of the displays are reduced which is useful especially in small portable terminals such as mobile phones.